(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Microscopic Effects of Stress on Platinum"

250 



Messrs. T. Andrews and C. B. Andrews. [Apr. 23, 



" Microscopic Effects of Stress on Platinum." By Thomas 
Andrews, F.B.S., F.C.S., and Charles Eeginald Andrews. 
Eeceived April 23, -Bead May 15, 1902. 

[Plate 4] 

The microscopic effects of stress on platinum do not appear to have 
been studied. An ingot of pure platinum was therefore prepared, and 
from this a portion was accurately machined in the form of a cube, 
0*30 inch square, which was afterwards carefully microscopically 
polished, and then subjected to compressive stress in the testing 
machine. 

Prior to the application of stress, and for comparative purposes, a 
polished face of the platinum cube was microscopically examined, but 
an even polished surface only was observed. A force producing a 
compression of 10 per cent, on the total height of the cube was then 
applied, and microscopic observations were taken at high magnifica- 
tions of the effects of the stress on the micro-crystalline structure of 
the platinum cube. The particulars of the stress applied are given 
on Table I. 



Table I. — Compressive Stress applied to Platinum Cube. 



Platinum cube. . 



Cross - 

section. 

Dimensions, 

inches. 



-30 x -29 



Area. 
Square 
inches. 



0-087 



Height 

before 

test. 

Inches. 



0-30 



Stress required to 

compress sample 

10 per cent, of 

its original height. 

Tons per square inch. 



12-82 



The polished side of the cube upon which the high-power micro- 
scopic examination was made was the one in line, or in parallel, with 
the direction of the compressive force. The results observed were 
very interesting, and confirm Professor Swing's and Mr. Rosenhain's 
observations on the peculiar manner in which the crystalline structure 
of a mass of metal becomes altered when under stress.* 

On comparing the appearance of the platinum after having been 
stressed with its appearance before the application of stress, it was 
found that many of the individual large or primary crystal grains 
forming the mass had, under the influence of the strain, developed 
innumerable fine " stress bands " or " slip bands," or indications of 
crystalline slip. The main lines of disruption were noticed in many 
instances to roughly approximate to an angle of about 45° to the 



Bakerian Lecture, 1899, ' Phil. Trans.,' A, vol. 193, 1900, p. 353. 



Andrews and Andrews. 



Roy. Soc. Proc, vol. 70, Plate 4. 



Fig. 1. 




Microscopic Effects of Compression Stress on Platinum, showing Crystalline Slip, as seen 
in Section. Magnification 120 diameters. Vertical illumination. Metal compressed 
10 per cent. Arrow indicates direction of compressive force. 











i- * 




Magnification 250 diameters. 



Magnification 120 diameters. 

Microscopic Effects of Compression Stress on Platinum, showing Crystalline Slip, as seen 
in Section. Vertical illumination. Metal compressed 10 per cent. Arrow indicates 
direction of compressive force. 



1902.] Microscopic Effects of Stress, on Platinum. 251 

line of the compressive force on the crystal sectional facets. Between 
these larger indications of crystalline slip were observed a number of 
extremely fine lines, indicative of the nature of the crystalline slip ; 
many of these ran more or less in parallel lines in each individual 
primary crystal or crystal grain, the direction of the orientation (or 
line of the normal cleavage) of each primary crystal grain apparently 
influencing the direction of the " slip bands," as seen in section. 

Owing to the varied orientation of the different crystals in the mass 
of the platinum,* the lines of cleavage as indicated by the minute 
" slip bands," were often seen at varied angles to the line of the 
straining force. 

These experiments have also confirmed the observations of Pro- 
fessor Ewing and others, that stress alone, without etching, sometimes 
renders manifest the lines of intercrystalline junction of the large or 
primary crystal grains of a stressed metal, providing that the stress is 
of sufficient intensity. This will be seen on reference to the accom- 
panying illustrations, Plate 4. 

The general appearance of the disintegration of the large or primary 
crystal grains, produced by the pressure, on the pure platinum cube, 
was the apparent breaking up of the crystalline structure of the 
metallic mass, as seen in section, roughly diagonally to the line of the 
compressive force. The area enclosed by the main lines of disruption 
roughly approximating to the size of the large primary crystal grains. 
The distances between the extremely fine lines, or " slip bands," ap- 
peared roughly to coincide proportionately with the size of the 
secondary or most minute crystals forming the mass, the finer "slip 
bands " appearing to indicate the crystalline slip which had taken 
place along the facets of the smaller or secondary crystals. The direc- 
tion, however, of the main lines of the crystalline disruption did not 
appear always to coincide with the intercrystalline facet junctions of 
the large or primary crystal grains. The lines of least resistance, or 
greatest crystalline slip, seemed chiefly to develop at an approximate 
angle of about 45 degrees to the pressure line, as previously men- 
tioned ; but the line of greatest weakness in the mass structure of 
the metal was not always at that angle with the line of the disruptive 
force. 

The previous description generally and approximately indicates the 
effect observed, but the breaking up of the crystalline structure of the 
metal appeared to be subject to modifications according to varied 
internal or external conditions. 

* See " Micro-crystalline Structure of Platinum," by Thomas Andrews, { Eoy. 
Soe. Proc.,' vol. 69 3 March 21, 1902, No. 457, p. 433 ; also "Microscopic 
Structure of Gold and Grold Alloys," by Thomas Andrews, l Engineering,' Septem- 
ber 30, October 28, December 9, 1898; also "Micro-metallography of Iron," by 
Thomas Andrews, * Eoy. Soc. Proc.,' toI. 58, 1895. 



252 Mr. W. Eosenhain. [May 1, 

The authors hope that these experiments may prove of use in afford- 
ing an indication of the comparative behaviour of this " apivTo-Kparia"' 
or noblest metal platinum, with the behaviour of the constructive 
metals, copper, nickel, iron and steel, when under the influence of 
stress ; and the experiments have also shown that the microscopic in- 
fluences of stress in the heavy metal platinum are analogous to those 
which have been observed in metals of lower specific gravity. 

DESCRIPTION OF PLATE. 

Fig. 1. — Microscopic Effects of Compression Stress on Platinum, showing Crystal- 
line Slip, as seen in Section. Magnification 120 diameters. Vertical 
illumination. Metal compressed 10 per cent. Arrow indicates direc- 
tion of compressive force. 

Fig. 2. — Microscopic Effects of Compression Stress on Platinum, showing Crystal- 
line Slip, as seen in Section. Magnification 120 diameters. Vertical 
illumination. Metal compressed 10 per cent. Arrow indicates direc- 
tion of compressive force. 

Fig. 3. — Same as fig. 2, but magnified 250 diameters. 



"A Note on the Eecrystallisation of Platinum." By Walter 
Eosenhain, B.A. (Cantab.), B.C.E. (Melbourne). Communi- 
cated by Professor Ewing, E.E.S. Eeceived May 1, — Eead 
May 15, 1902. 

In a recent paper* Professor Ewing and the present author have 
described phenomena of recrystallisation in a number of metals, such 
as lead, tin, zinc, and cadmium, at temperatures well below the melting 
points of those metals. I have recently observed phenomena which 
appear to me to be of a very similar nature in the case of platinum. 

It is a well-known fact that a prolonged exposure to a high tempera- 
ture renders platinum brittle, and that the surface of such platinum,, 
when it has been exposed to flame, shows markings " resembling the 
appearance of galvanised iron." f This phenomenon has generally been 
ascribed to the action of carbon, and by one author specifically to the 
action of acetylene. f Having studied the phenomena closely with the 
aid of the microscope, I do not find this view entirely confirmed. 

In the first place, on examining the surface of the "changed" 
platinum with the microscope, it is seen to show a pattern which is 

* " % On the Crystalline Structure of Metals," second paper, ' Phil. Trans.,' A, . 

1900, vol. 195, pp. 279—301. 

f "The Action of the Acetylene Flame on Platinum," J. J. Eedwood, ' Soc. 
Chem. Industry Journ.,' vol. 17, p. 1107; also ' Zeitschrift fur Analyt. Oh em.,' 

1901, heft 6, p. 411. 




Microscopic Effects of Compression Stress on Platinum, showing Crystalline Slip, as seen 
in Section. Magnification 120 diameters. Vertical illumination. Metal compressed 
10 per cent. Arrow indicates direction of compressive force. 




Magnification 120 diameters. Magnification 250 diameters. 

Microscopic Effects of Compression Stress on Platinum, allowing Crystalline Slip, as seen 
in Section, Vertical illumination. Metal compressed 10 per cent. Arrow indicates 
direction ol compressive force.